DESCRIPTION: The goal of this research is to investigate the distribution of the epithelial sodium channel subunits involved in salt taste in relation to a and species differences in gustatory sodium sensitivity. Previous recordings from the whole chorda tympani (CT) nerve in rats and hamsters indicate opposit developmental patterns in gustatory sodium sensitivity -- young rats are more sensitive than mature rats, whereas young hamsters are less sensitive than mature hamsters. The first specific aim is to analyze the difference between young and adult hamsters using single fiber recording techniques. Complementa studies on the rat are currently in progress. The stimulation device allows chemical stimuli to be presented to taste receptors in a patch of lingual epithelium under voltage clamp while recording from a single chorda tympani nerve axon. Data on the voltage sensitivity of the CT response are then used derive estimates on the affinity and density of the epithelial sodium channel, as demonstrated in previously published studies. The hypothesis is that, compared to young hamsters, mature animals will show reduced sodium response frequencies, fewer fibers that are most responsive to sodium, and lower estimates of channel affinity and/or density. The second aim is to employ recently developed antisera to immunohistochemically identify the subunits of the epithelial sodium channel involved in taste transduction in young and matu hamsters and rats. Fluorescence microscopy will be used to examine the distribution of immunoreactivity within the taste buds to antisera for the alpha, beta, and gamma subunits of the sodium channel. The hypothesis is that the age and species differences in chorda tympani sodium sensitivity will be reflected in corresponding differences in the expression and distribution of t channel subunits.